USRP python problem

Hi,

I am trying to output the data of constellation sink to a file. Since
constellation sink has some synchronization process in the block, which
shows me a better constellation points compared to scope.

My gnuradio version is: V3.2.2. The constellation python code is located
at:
/usr/lib/python2.6/dist-packages/gnuradio/wxgui/constsink_gl.py
At the sink of constsink_gl code, it seems like trying to output the I &
Q
information to the queue, name “msgq” at line 96.

The result I output is: <input_watcher(Thread-2, started daemon
-1325728880)>

How can I output the value before plotting in the window?

Many thanks for any suggestions!